Electronic Device Having Force Sensor Air Flow Promotion Structures

ABSTRACT

An electronic device such as a device with a display may have a force sensor. The force sensor may include capacitive electrodes separated by a deformable layer such as a layer of an elastomeric polymer. The display or other layers in the electronic device may deform inwardly under applied force from a finger of a user or other external object. As the deformed layers contact the deformable layer, the deformable layer is compressed and the spacing between the capacitive electrodes of the force sensor decreases. This causes a measurable rise in the capacitance signal and therefore the force signal output of the force sensor. To prevent the deformable layer from sticking to the inner surface of the display layers, air flow promotion structures may be interposed between the deformable layer and the inner surface of the display. The air flow promotion structures may include spacer pads with anti-stick surfaces.

This application claims the benefit of provisional patent applicationNo. 62/206,428, filed Aug. 18, 2015, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

This relates generally to electronic devices and, more particularly, toelectronic devices with force sensors.

Electronic devices such as laptop computers may be provided withdisplays to provide visual output and track pads and other devices togather touch and force input from a user. In some electronic devicessuch as tablet computers and cellular telephones, touch screens are usedto display visual information and gather touch input.

There are challenges associated with implementing sensors such as forceand touch sensors in an electronic device. If care is not taken, sensormeasurements may be less accurate than desired or devices may be morebulky than desired.

It would therefore be desirable to be able to provide improved sensorarrangements for electronic devices.

SUMMARY

An electronic device such as a device with a display may have a forcesensor. The force sensor may include capacitive electrodes separated bya deformable layer such as a layer of an elastomeric polymer. Theelectrodes may include an upper set of electrodes formed in an arraypattern and a lower electrode on an opposing surface of the elastomericpolymer layer. Force sensor circuitry may make capacitance measurementsbetween the capacitor electrode structures on the opposing surfaces ofthe elastomeric layer.

The display may have a backlight unit and a display module that isbacklit by the backlight unit or may have other display layers. Thedisplay layers or other layers in the electronic device may bendinwardly under force from a finger of a user or other external objectapplied to the surface of the display or other external surface of theelectronic device. These layers may be separated from the deformablelayer by an air gap. When bent inwardly, the bent layers may come intocontact with the deformable layer.

As the bent layers contact the deformable layer, the deformable layerbecomes compressed and the spacing between the capacitive electrodes ofthe force sensor decreases. This causes a measurable rise in thecapacitance associated with the electrodes and therefore a rise in theforce signal output of the force sensor. When the user's finger isreleased from the bent layers or the applied external force is otherwiseremoved, the bent layers will experience a restoring force that movesthe bent layers outwardly toward their original (unbent) position.

To prevent the deformable layer from sticking to the contacting surfaceof the display layers as a result of smooth-surface-to-smooth-surfacecontact and/or due to adhesion of the contacting layers to each other,air flow promotion structures may be interposed between the deformablelayer and the contacting surface of the display layer. The air flowpromotion structures may include spacer pads and anti-stick surfaces.The spacer pads may create air flow channels to help ensure adequate airflow into the air gap between the display layers and deformable layer asthe display layers spring back to their original (unbent) position. Theanti-stick surfaces may include textured surface structures andhydrophobic coatings to reduce adhesion to the display layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device inaccordance with an embodiment.

FIG. 2 is a schematic diagram of an illustrative electronic device inaccordance with an embodiment.

FIG. 3 is a top view of an illustrative touch sensor in accordance withan embodiment.

FIG. 4 is a top view of an illustrative touch sensor electrode patternin accordance with an embodiment.

FIG. 5 is a cross-sectional side view of an illustrative force sensor ina configuration in which a user's finger has not contacted the sensor inaccordance with an embodiment.

FIG. 6 is a cross-sectional side view of the illustrative force sensorof FIG. 5 following depression of the surface of the force sensor withthe user's finger in accordance with an embodiment.

FIG. 7 is a cross-sectional side view of an illustrative device with aforce sensor that is not being contacted by an external object such as auser's finger in accordance with an embodiment.

FIG. 8 is a cross-sectional side view of the illustrative device of FIG.7 following application of pressure on the force sensor with the fingerof the user or other external object in accordance with an embodiment.

FIG. 9 is a graph showing how an output signal from a force sensor maybe affected by the presence of air-flow promotion structures and otherstructures that promote the release of adjacent layers within a forcesensor in accordance with an embodiment.

FIGS. 10 and 11 are cross-sectional side views of illustrative air flowpromotion structures to promote air flow within a force sensor andthereby enhance force sensor responsiveness in accordance with anembodiment.

FIGS. 12-17 are top views of illustrative spacer pad patterns of thetype that may be used in air flow promotion structures in an electronicdevice with a force sensor in accordance with an embodiment.

FIGS. 18-21 are top views of illustrative air flow promotion structuresshowing possible relationships between the size of spacer pads in theair flow promotion structures and electrodes on a deformable layer in aforce sensor in accordance with an embodiment.

FIG. 22 is a cross-sectional side view of an illustrative spacer pad ina configuration in which the surface of the spacer pad has been providedwith a texture to minimize sticking to adjacent layers in accordancewith an embodiment.

FIG. 23 is a top view of an illustrative spacer pad with texturedanti-stick structures to prevent sticking in accordance with anembodiment.

FIG. 24 shows how a spacer pad may have an undulating surface texture toprevent sticking in accordance with an embodiment.

FIG. 25 is a cross-sectional side view of an illustrative spacer padwith an anti-stick surface coating to help prevent sticking inaccordance with an embodiment.

FIG. 26 is a cross-sectional side view of an illustrative display withair flow promotion structures formed from recesses in structures belowan air gap in accordance with an embodiment.

FIG. 27 is a cross-sectional side view of an illustrative display withair flow promotion structures formed from surface deformations onstructures above an air gap in accordance with an embodiment.

FIG. 28 is a cross-sectional side view of an illustrative display withair flow promotion structures formed from surface deformations onstructures below an air gap in accordance with an embodiment.

FIG. 29 is a cross-sectional side view of an illustrative layer that hasair flow promotion structures formed from holes that pass through sensorelectrodes in accordance with an embodiment.

DETAILED DESCRIPTION

An electronic device such as electronic device 10 of FIG. 1 may havesensors such as force and touch sensors and a display such as display14. The sensors of device 10 may be integrated with display 14 (e.g.,display 14 may include a touch sensor and force sensor that overlaps thepixels of display 14) and/or device 10 may have a trackpad or otherstructure that gathers force and/or touch sensor input on a portion ofdevice 10 that is separate from display 14. Illustrative configurationsfor device 10 in which touch and/or force input is gathered by touchingand pressing against display 14 are sometimes described herein as anexample.

Device 10 may be a handheld electronic device such as a cellulartelephone, media player, gaming device, or other device, may be a laptopcomputer, tablet computer, or other portable computer, may be a desktopcomputer, may be a computer display, may be a display containing anembedded computer, may be a television or set top box, may be a tabletcomputer that is attached to a detachable cover with a keyboard or otheraccessory, or may be other electronic equipment.

As shown in the example of FIG. 1, device 10 may have a housing such ashousing 12. Housing 12 may be formed from plastic, metal (e.g.,aluminum), fiber composites such as carbon fiber, glass, ceramic, othermaterials, and combinations of these materials. Housing 12 or parts ofhousing 12 may be formed using a unibody construction in which housingstructures are formed from an integrated piece of material. Multiparthousing constructions may also be used in which housing 12 or parts ofhousing 12 are formed from frame structures, housing walls, and othercomponents that are attached to each other using fasteners, adhesive,and other attachment mechanisms.

Device 10 may have a display such as display 14 mounted in housing 12.Display 14 may be formed using any suitable display technology. Forexample, display 14 may be liquid crystal display (LCD), a plasmadisplay, an organic light-emitting diode (OLED) display, anelectrophoretic display, a microelectromechanical systems (MEMs) shutterdisplay, or a display implemented using other display technologies.

A touch sensor and a force sensor may be incorporated into display 14.Touch sensors for display 14 may be resistive touch sensors, capacitivetouch sensors, acoustic touch sensors, light-based touch sensors,force-based touch sensors, or touch sensors implemented using othertouch technologies. As an example, device 10 may include a capacitivetouch sensor with an array of capacitive touch sensor electrodes thatallows measurement of the position of an external objected such asfinger 20. The touch sensor may determine where an external object suchas a user's finger (e.g., finger 20) is contacting the surface of device10 and display 14 (i.e., the touch sensor may measure the location atwhich an external finger contacts the surface of display 14 in lateraldimensions 18). Display 14 lies within the X-Y plane of FIG. 1, so thetouch sensor output from the touch sensor of display 14 producesinformation on the position of the user's finger (or other externalobject) in lateral dimensions X and Y.

When an external object such as finger 20 presses downwards on display14 (or other external surface of device 10) in direction 22, force isimparted on the surface of display 14 (or other device structure).Display 14 may include force sensor structures that detect force ondisplay 14 in direction 22 (i.e., in the −Z direction of FIG. 1). Withone suitable arrangement, display 14 includes an outer transparent layer(sometimes referred to as a display cover layer). The display coverlayer may be formed from a material such as glass, plastic, sapphire, orother transparent material. The display cover layer is clear, so thatdisplay 14 may display images for a user using an array of pixelsoverlapped by the display cover layer. The display cover layer or otherplanar member in device 10 (e.g., a trackpad member) may deform out ofthe X-Y plane when force is exerted in direction 22.

A force sensor may be implemented using capacitive sensor electrodeswithin device 10. The force sensor may be formed on the underside ofdisplay 14 or may be formed on layers of material that are separatedfrom display 14 by an air gap.

Capacitances associated with the electrodes in the force sensor may varyas a function of separation between the electrodes, which can beinfluenced by the amount of force applied to the force sensor bypressing on display 14 or other structures in device 10. Forcemeasurements may therefore be gathered by making capacitancemeasurements between appropriate capacitor electrodes. If desired, thesecapacitance measurements may also be processed to determine the positionat which a force is being applied to device 10 (i.e., to covert forcedata into touch location data). In this way, force data may be used toimplement a touch sensor.

Illustrative configurations for the force and touch sensing structuresof device 10 may sometimes be described herein in the context of touchand force sensors integrated into display 14. This is, however, merelyillustrative. Touch and/or force sensors may be incorporated into otherportions of device 10 (e.g., portions of device 10 that do not includedisplay structures), if desired.

A schematic diagram of an illustrative electronic device such as device10 of FIG. 1 is shown in FIG. 2. As shown in FIG. 2, electronic device10 may have control circuitry 24. Control circuitry 24 may includestorage and processing circuitry for supporting the operation of device10. The storage and processing circuitry may include storage such ashard disk drive storage, nonvolatile memory (e.g., flash memory or otherelectrically-programmable-read-only memory configured to form a solidstate drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Processing circuitry in control circuitry 24may be used to control the operation of device 10. The processingcircuitry may be based on one or more microprocessors, microcontrollers,digital signal processors, baseband processors, power management units,audio chips, application specific integrated circuits, etc.

Input-output circuitry in device 10 such as input-output devices 26 maybe used to allow data to be supplied to device 10 and to allow data tobe provided from device 10 to external devices. Input-output devices 26may include buttons, joysticks, scrolling wheels, touch pads, key pads,keyboards, microphones, speakers, tone generators, vibrators, cameras,sensors, light-emitting diodes and other status indicators, data ports,etc. A user can control the operation of device 10 by supplying commandsthrough input-output devices 26 and may receive status information andother output from device 10 using the output resources of input-outputdevices 26. Input-output devices 26 may include one or more displayssuch as displays 14.

Control circuitry 24 may be used to run software on device 10 such asoperating system code and applications. During operation of device 10,the software running on control circuitry 24 may display images ondisplay 14 (e.g., video, still images such as text, alphanumeric labels,photographs, icons, other graphics, etc.) using arrays of pixels indisplay 14.

Display 14 may have a rectangular shape or other suitable shape. Forexample, display 14 may have a rectangular footprint and a rectangularperipheral edge that runs around the rectangular footprint. Display 14may be planar or may have a curved profile.

Touch sensor 28 may be implemented using an array of capacitiveelectrodes (e.g., electrodes that extend across the surface of device 10in dimensions X and Y. The touch sensor may be formed as part of a trackpad or other structure that is independent from display 14 or may beincorporated into one of the layers of display 14. In configurations inwhich touch sensor 28 is incorporated into the structures of display 14,capacitive touch sensor electrodes for sensor 28 may be formed from atransparent material such as indium tin oxide.

Force sensor 30 may be implemented in an opaque structure such as atrack pad in display 14 and/or may be implemented as part of display 14.Force sensor 30 may be formed from capacitive electrodes that produce acapacitance output that is indicative of applied force or may beimplemented using other force sensor technologies. If desired, some ofthe capacitive electrodes that are used in forming force sensor 30 maybe shared with some of the capacitive electrodes that are used informing touch sensor 28. Configurations in which the sensor electrodesfor measuring touch sensor input and force sensor input are separate mayalso be used.

In some configurations, force sensor signals from an array of forcesensor electrodes may be processed provide information on the locationat which finger 20 is applying force, thereby allowing force sensor 30to serve as a touch sensor (in addition to serving as a force sensorthat produces force output data proportional to the amount of forceapplied by finger 20 in inward direction 22).

Configurations in which touch sensor 28 and force sensor 30 areimplemented using transparent capacitive touch sensor electrodes thatoverlap display 14 are sometimes described here as an example. Othertouch sensor and force sensor arrangements may be used in device 10, ifdesired.

FIG. 3 is a top view of an illustrative capacitive touch sensor. Asshown in FIG. 3, touch sensor 28 may have overlapping electrodes such aselectrodes 36 and electrodes 38. Electrodes 36 and 38 may be coupled totouch sensor circuitry such as touch sensor controller 34. Controller 34may apply drive signals to electrodes 36 while gathering correspondingsense signals from electrodes 38. In the presence of an external objectsuch as finger 20 at an intersection between a particular one ofelectrodes 36 and a particular one of electrodes 38, the capacitancesensed between the intersecting electrodes will change. By processingthe drive and sense signals, controller 34 can monitor the capacitancesbetween each of the intersecting electrodes in sensor 38 and therebydetermine whether or not those electrodes are being touched by finger20. This allows the position of finger 20 to be determined by controller34.

In the example of FIG. 3, electrodes 36 and 38 have the shape ofelongated strips of conductive material (e.g., indium tin oxide, etc.).Other electrode shapes may be used if desired (e.g., blanket films,patterns of diamond-shaped or rectangular electrodes, etc.). In theillustrative electrode pattern of FIG. 4, electrode 36 is a blanketconductive layer (e.g., an electrode that overlaps all of display 14)and electrodes 38 are patterned to from an array of rectangular pads.Other electrode patterns may be used, if desired. The illustrativecapacitive touch sensor electrode patterns of FIGS. 3 and 4 are merelyexamples.

FIGS. 5 and 6 show how force sensor 30 may use a capacitive sensorarrangement. In the example of FIG. 5, sensor 30 has upper (outer) forcesensor capacitive electrode 40 and lower (inner) force sensor capacitiveelectrode 44. Dielectric material 42 (e.g., an elastomeric polymer orother deformable layer) may be interposed between electrodes 40 and 44.Controller 46 may measure the capacitance between electrodes 40 and 44.Capacitance is at a minimum when the separation between electrodes 40and 44 is a maximum, as shown in FIG. 5. After a user has pressed finger20 inwards in direction 22 as shown in FIG. 6, upper electrode 40deforms towards electrode 44, thereby increasing the amount ofcapacitance measured by controller 46. With this type of arrangement,the capacitance output of sensor 30 is proportion to force. Capacitanceis low when applied force is low and is high when applied force is high.

It may be desirable to form a touch sensor such as touch sensor 28 and aforce sensor such as force sensor 30 from structures in display 14.Consider, as an example, the cross-sectional side view of the portion ofdevice 10 that is shown in FIG. 7. As shown in FIG. 7, display 14 mayinclude an outer layer such as display cover layer 50. Displaystructures 52 may be attached to the lower surface of display coverlayer 50. Display structures 52 may include, for example, an organiclight-emitting diode layer, a liquid crystal display layer, and/or othertypes of display structures for producing images for a user. A touchsensor may be formed within layers 52 or may be formed elsewhere indevice 10. With one illustrative configuration, display structures 52include liquid crystal display layers (module) 52A and backlight unit52B.

Module 52A may have upper (outer) and lower (inner polarizers) andinterposed layers such as a color filter layer, liquid crystal layer,and thin-film transistor layer. Capacitor electrode 56 may be located onthe inner surface of the inner polarizer layer and may overlap display14.

Backlight unit 52B may be located below electrode 56. Backlight unit 52Bmay be formed from a light guide layer that receives light fromedge-mounted light-emitting diodes. The light guide layer distributesthe light laterally throughout display 14. Light that is scatteredoutwards through module 52A may serve as backlight illumination fordisplay 14. Light that is scattered inwards may be reflected upwards bya reflector located on the bottom surface of backlight unit 52B.

Capacitive electrodes 60 may be formed in an array (e.g., atwo-dimensional array) that covers display 14. Elastomeric layer 62 maysupport electrodes 60. An air gap such as air gap 64 may lie betweenelectrodes 60 and backlight unit 52B. Elastomeric layer 62 may separatelower capacitive electrode 66 from electrodes 60 by a distance D1 whenfinger 20 is not pressing inwardly on display cover layer 50. Dielectriclayers 68 (e.g., polymer layer(s)) may separate ground layer 70 fromlower electrode 66. Additional structures such as structures 72 mayserve as support structures for the layers of material mounted abovestructures 72. Structures 72 may include, for example, pressuresensitive adhesive, battery structures, housing structures, etc.

During operation of the force sensor, control circuitry such ascircuitry 46 of FIGS. 5 and 6 may measure capacitances using thecapacitive electrodes of device 10. As an example, force sensorcircuitry such as circuitry 46 may monitor capacitances betweenelectrodes 60 on the upper surface of deformable elastomeric layer 62and electrode 66 on the lower surface of deformable elastomeric layer62.

When finger 20 presses downward in direction 22, display cover layer 50may deform inwardly so that backlight unit 52B and other displaystructures 52 press against the upper surface of elastomeric layer 62and thereby deform elastomeric layer 62 inwardly, as shown in FIG. 8.This reduces the distance separating electrodes 60 from lower electrode66 from D1 in FIG. 7 to a value D2 that is less than D1 in FIG. 8. Asthe separation between electrodes 60 and electrode 66 decreases,controller 46 may measure correspondingly increased capacitance(s)between each displaced electrode 60 and electrode 66, thereby producingan output that is proportional to force. The output can be obtainedindependently for each deflected electrode 60 or the maximum output ofelectrodes 60 or other collective output signal may be gathered. Inconfigurations in which a force signal is gathered from each electrode60 force data may be converted to position information (e.g., the forcesensor structures may be used in producing position data that cancomplement or replace the position data produced using touch sensor 28).If desired, controller 46 may measure other capacitance values (e.g.,the capacitance between upper electrode 56 and electrodes 60 may bemeasured, which is also indicative of applied force levels).

Touch sensor structures for display 14 may be formed from an array oftouch sensor electrodes in display structures 52 (e.g., electrodes indisplay module 52A), from an array of touch sensor electrodes interposedbetween display module 52A and the inner surface of display cover layer50, or other capacitive touch sensor electrodes that are separate fromthe force sensor electrodes and/or force sensor electrodes such aselectrode 56, electrodes 60, and/or electrode 66 may be used in forminga capacitive touch sensor.

As shown in FIG. 8, the lower portion of display 14 (i.e., inner surface76 of backlight unit 52B) may press inwardly against layer 62 andelectrodes 60 when finger 20 presses inwards in direction 22 and deforms(i.e., bends) display 14. This forces the air from air gap 64 to moveoutwards from under display 14 in directions 78. When finger 20 isreleased from display cover layer 50 in direction 74, the depressedportion of display cover layer 50 will move in direction 74 to return toits original shape (e.g., a planar shape). Display cover layer 50 willmove in direction 74 to relieve the stress that was imparted to layer 50when layer 50 was bent due to the pressure of finger 20 in direction 22.Elastomeric layer 62 may also exert a restoring force on display layer50 in direction 74 and will restore electrodes 60 to their initialposition. The spring-back force imparted in direction 74 by displaycover layer 50 will pull the lower surface of display 14 (e.g.,backlight 52B) away from electrodes 60 and layer 62. As a result, theair that was displaced from under display cover layer 50 to air gapregions 64′ will be drawn back under display cover layer 50 indirections 80.

The air flow in directions 80 that is created by the release of finger20 from display cover layer 50 is impeded by the small separationbetween the lower surface of display 14 (e.g., the lower surface ofbacklight 52B) and the upper surface of the adjacent portions of thestructures of FIG. 8 such as electrodes 60 and elastomeric layer 62.Particularly in configurations in which these two mating surfaces aresmooth, there is a risk that the gap size (the height of adjacent airgap portions 64′ and the air gap directly under the primary deformedportion of display cover layer 50) will be so small that air cannotreadily return to fill air gap 64. This blocks airflow and slows downthe process of returning display 14 and air gap 64 to their normalstates.

In addition to slowing movement of the bent display layers of display14, suction arising from the small air gap can produce force sensorhysteresis. In particular, upward movement of display 14 as display 14is springing back to its original position may create suction thatmomentarily pulls upon layer 62 and electrodes 60. This upward pull onlayer 62 tends to separate electrodes 60 from electrode 66, therebycreating an overshoot condition characterized by an overly small outputcapacitance measured across electrodes 66 and 60. One of theconsequences of inadequate airflow in regions 64′ (and/or stickiness ofthe bent display layers with respect to layer 62) is therefore anovershoot in the force signal.

To minimize or eliminate force sensor signal overshoot, air flowpromotion structures may be formed on electrodes 60 and the uppersurface of layer 62. By promoting air flow and reducing sticking betweenlayer 62 and the lower surface of display 14, display cover layer 50 mayreturn upwards to its planar configuration rapidly after finger 20 isremoved. The air flow promotion structures may be reduce or eliminateupwards suction on electrodes 60 during this process. The air flowpromotion structures may include rectangular spacers (sometimes referredto as shims, pads, or spacer pads) that prevent uninterrupted intimatecontact between large smooth portions of display 14 and layer 62 whendisplay 14 is bent inwardly to compress layer 62. Anti-stick coatings,textures, and other features may be incorporated into the air flowpromotion structures to enhance performance.

The impact of incorporating air flow promotion structures betweenelectrodes 60 and the lower surface of display 14 is illustrated in thegraph of FIG. 9. In the graph of FIG. 9, force sensor output F (e.g.,the capacitance between one or more of electrodes 60 and electrode 66)has been plotted as a function of time for two different illustrativeforce sensor configurations. Dashed line 84 corresponds to a forcesensor configuration of the type shown in FIG. 8 without any air flowpromotion structures interposed between display 14 and electrodes 60.Solid line 86 corresponds to a force sensor configuration in which airflow promotion structures have been incorporated onto the lower surfaceof display 14 and/or the opposing upper surface of electrodes 60 andlayer 62.

At time t1, a user of device 10 presses inwards in direction 22. Thiscauses display 14 to bridge air gap 64 and press electrodes 60 inwardlytowards electrode 66. The output of the force sensor (i.e., thecapacitance between electrode(s) 60 and electrode 66 therefore increasesfrom low level FL to high level FH. The magnitude of force sensor outputsignal (capacitance) FH is proportional to the force exerted on display14 (i.e., FH is inversely proportional to the distance separatingelectrodes 60 from electrode 66).

At time t1, the user releases finger 20 and display 14 springs upwardsin direction 74. Air flows under the released portion of display 14 indirections 80. In the presence of air flow promotion structures, display14 quickly returns to its normal planar state (or other resting state)and force signal F (i.e., the capacitance between electrodes 60 andelectrode 66) drops quickly to low level FL, as illustrated by solidline 86 of FIG. 9. In the absence of air flow promotion structures, incontrast, the narrow size of gap 64′ and the smooth and intimate contactbetween display 14 and electrodes 60 slows air flow and creates upwardssuction on electrodes 60 and surface stickiness, momentarily pullingelectrodes 60 away from electrode 66 and creating an abnormally lowforce output signal F (see, e.g., overshoot 84′ in line 84 of FIG. 9).

Illustrative air flow promotion structures are shown in FIG. 10. In theexample of FIG. 10, air flow promotion structures 90 have been formed onlower layer 62 (e.g., an elastomeric support for electrodes 60, whichare not shown in FIG. 10). If desired, air flow promotion structures 90may be formed on the opposing lower surface of backlight unit 52B or airflow promotion structures 90 may be formed on both of the opposingsurfaces facing air gap 64 (i.e., the lower surface of backlight unit52B and the opposing upper surface of electrode support structures suchas layer 62). Configurations in which air flow promotion structures 90are formed on layer 62 are sometimes described herein as an example.

In the illustrative configuration of FIG. 10, air flow promotionstructures 90 include an array of pads (sometimes referred to asspacers, spacer pads, or shims) separated by interposed air flowchannels 96. The spacer pads may all have the same height, may havethree or more different heights, or, as shown in FIG. 10 structures 90may include pads of two different heights (i.e., two differentthicknesses) such as tall pads 90-1 and short pads 90-2. Configurationswith multiple different heights may help promote quick release of thelower surface of display 14 from layer 62 and satisfactory air flow.

Pads 90-1 and 90-2 may be formed from layers of polymer or othermaterials (layers 92) that have been attached to layer 62 using adhesive94. In this type of arrangement, pads 90-1 and 90-2 may be attached tolayer 62 from a tape (as an example). If desired, pads such as pads 90-1and 90-2 (or other spacer structures that promote air flow) may bedeposited using screen printing, blanket deposition of a layer or layersof material followed by photolithographic patterning (e.g., a layer ofphotoimageable polymer exposed and developed to form a desired padpattern), blanket deposition followed by etching, shadow-maskdeposition, electroplating, or other techniques for forming pads 90-1and 90-2 from a single material or layers of material. Configurationsfor air flow promotion structures 90 that are formed from three or moredifferent materials (e.g., an adhesive layer, a stiff polymer shim padlayer, and a non-stick coating) may also be used.

Air flow promotion structure pads 90-1 and 90-2 may be organized in arectangular array having rows and columns or may be arranged in otherpatterns. A top view of air flow promotion structures 90 of FIGS. 10 and11 is shown in FIG. 12. As shown in FIG. 12, air flow promotionstructures 90 may include pads 90-1 and 90-2. The heights of pads 90-1and 90-2 causes pads 90-1 and 90-2 to protrude upwards away from layer62 and prevents the lower surface of backlight unit 52B from contactinglayer 62. When display cover layer 50 is released and is springing backtowards its planar configuration, air may flow through structures 90 inair flow channels such as channels 96 of FIG. 12 and over the pads(particularly shorter pads 90-2, as illustrated by arrow 98 of FIG. 12).Because of the uneven surface formed by air flow promotion structures 90(and the reduced amount of area where the display layers and layer 62contact each other), display cover layer 50 and layer 62 will be able topull apart from each other without excessive resistance (i.e., air willbe able to flow quickly in directions 80, thereby avoiding overshoot inforce output signal F).

In the illustrative arrangement of FIG. 12, tall spacer pads 90-1 andshort spacer pads 90-2 are arranged in a checkerboard pattern(alternating across both rows and columns of the array of pads). FIG. 13shows how pads 90-1 and pads 90-2 may be arranged in alternatingcolumns. In the configuration of FIG. 14, pads 90-1 and pads 90-2 arearranged in a checkerboard pattern and have different shapes. Pads 90-1are rectangular. Pads 90-2 are diamond shaped. In the illustrativecheckerboard pattern of FIG. 15, pads 90-1 and pads 90-2 are circular.FIG. 16 shows how pads 90-1 and 90-2 may be elliptical. In the exampleof FIG. 17, pads 90-1 and 90-2 are triangular. The shape of the channels96 surrounding each cluster of six pads 90-1 and 90-2 of the type shownin FIG. 17 is hexagonal. In general, the pads of air flow promotionstructures 90 may be triangular, rectangular, circular, elliptical,square, hexagonal, may have shapes with curved sides, shapes withstraight sides, and shapes with combinations of straight and curvedsides, may form grooves, may form recesses, may form arrays and haveother regular patterns, may be arranged in pseudorandom patterns, or mayhave other suitable configurations. The configurations of FIGS. 10-17are merely illustrative.

As shown in FIG. 18, air flow promotion pads 90P in air flow promotionstructures 90 may be smaller than electrodes 60 and may be overlapped byelectrodes 60. Electrodes 60 may be formed from an array of rectangularpads (e.g., metal pads) or other suitable electrode structures. In theexample of FIG. 19, air flow promotion structure pad 90P has the samerectangular shape and same size as electrode 60. FIG. 20 shows how airflow promotion structure pad 90P may be larger than electrode 60. In theFIG. 21 example, there are four pads 90P on a single correspondingelectrode 60. Configurations in which pads 90P partly overlap electrodes60 and/or are spaced unevenly with respect to electrodes 60 may also beused.

It may be desirable to texture pads 90P, as shown in FIG. 22. In theexample of FIG. 22, upper surface 90P′ of spacer pad 90P has beenprovided with protruding portions 100 that are separated by recessedportions 102. The surface texture associated with upper surface 90P′ mayhelp prevent sticking between the lower surface of display 14 and theupper surface of the air flow promotion structures on layer 62 and maytherefore be referred to as an anti-stick surface, anti-stickstructures, or anti-stick texture.

FIG. 23 is a top view of the illustrative anti-stick structures of FIG.22 showing how protrusions 100 may have rectangular shapes and may bearranged in an array with rows and columns. Other configurations may beused for protrusions 100 (e.g., triangular shapes, rectangular shapes,protrusions with different heights, circular shapes, elliptical shapes,shapes with straight edges, curved edges, or combinations of strait andcurved edges, shapes in pseudorandom patterns, etc.). Thecross-sectional side view of FIG. 24 shows how protrusions 100 may havea wavy profile. Protrusions 100 may be formed using embossing, etching,molding, photolithography, or other techniques.

A non-stick coating layer such as a layer of polytetrafluoroethylene orother non-stick coating may be formed on the upper surface of a texturedor smooth spacer pad, as shown by illustrative non-stick coating 104 onpad 90P of air flow promotion structures 90 of FIG. 25.

To prevent air flow promotion structures 90 from deforming excessivelyand thereby tending to stick when contacted by display cover layer 50 orother surfaces, it may be desirable to form air flow promotionstructures 90 (e.g., spacer pads, etc.) from stiff materials (e.g.,materials such as plastic, metal, glass, ceramic, or other materialshaving an elastic modulus of 0.5 GPa or more, 1 GPa or more, 1-100 GPa,more than 2 GPa, less than 200 GPa, or other suitable value). When airflow prevention structures 90 are formed from stiff materials such asthese, downwards force from display cover layer 50 may be transferred todeformable elastomeric layer 62, so that electrodes 60 and layer 62 aredeformed downwards without expending downwards force from finger 20compressing the material of structures 90. Stiff air flow preventionstructures are therefore able to efficiently transfer force from finger20 to electrodes 60.

The height of air flow prevention structures 90 (e.g., the heights oftall and short spacer pads) may be about 20-50 microns, more than 5microns, more than 10 microns, more than 20 microns, 10-150 microns,less than 200 microns, more than 30 microns, less than 75 microns, orother suitable height. This helps allow sufficient air to flow withoutcreating excess thickness in the layers of device 10.

The ratio of the area consumed by the spacer pads to the air flowchannels surrounding the spacer pads may be 1:1, 1-100 to 1, more than 1to 1, more than 2 to 1, more than 100 to 1, less than 100 to 1, lessthan 2 to 1, less than 1 to 1, 1 to 1-100, 1 to 2-20, 1 to more than 1,1 to more than 10, 1 to more than 100, or 1 to less than 50 (asexamples). When relatively more area is consumed by spacer pads, forcetransfer is enhanced, but air flow can become restricted. Whenrelatively more area is consumed by air flow channels, air flow isenhanced, but excessively small spacer pad areas should be avoided toensure that there is sufficient contact area to deflect electrodes 60satisfactorily.

The surface characteristics of the spacer pads in air flow promotionstructures 90 can be selected to reduce sticking and thereby help avoidsensor overshoot. Stickiness can be reduced by creating a texture on theupper surface of the spacer pads and/or by applying a non-stick coatingto the spacer pads. Textured surfaces are illustrated in the examples ofFIGS. 22-24. A non-stick coating is illustrated by coating 104 of FIG.25. Non-stick coatings for structure 90 may by hydrophobic. Examples ofnon-stick (hydrophobic) coating materials for structures 90 includepolytetrafluoroethylene and fluorinated ethylene propylene. Hydrophobiccoating materials for use in coating air flow promotion structures 90may be characterized by relatively large contact angles A (e.g., contactangle A may be greater than 90°, contact angle A may be greater than130°, or contact angle A may be greater than 170°). Non-stick coatingsmay be formed on spacer pads with smooth or textured surfaces.

FIG. 26 is a cross-sectional side view of display 14 in an illustrativeconfiguration in which air flow promotion structures have been formed byforming openings 202R in layer 202. Layer 202 may include some or all ofthe layers below air gap 64 such as the layers forming electrodes 60and/or 66 and/or layers 62, 68, 70, and 72 of FIGS. 7 and 8 and may beseparated from display structures 52 (e.g., layer 200) by air gap 64.Openings 202R may pass through all of layer 202 as shown by illustrativeopenings 202R′ or may protrude only partway through layer 202 as shownby illustrative recesses 202R″. Openings 202R may be formed throughelectrodes such as electrodes 60 and/or 66, may be formed in gapsbetween electrodes, and/or may be formed in other portions of layer 202.

Protruding portions 202P of layer 202 are formed between respectiveopenings 202R and may form spacer pads, texture on a spacer pad, orother air flow promotion structures. Recesses 202R in layer 202 may beformed by punching, laser drilling, machining, photolithography, orother suitable fabrication techniques. Openings 202R may be patterned toform circular openings, square openings, grooves, slots, air channels,and/or other air flow promotion shapes of the type described inconnection with 10-23. Openings 202R may be formed in non-sensingportions of layer 202 or other portions of layer 202. Openings such asopenings 202R in lower layer 202 may be formed in one or more of thelayers of material above air gap 64 (see, e.g., display structures 52).The example of FIG. 26 in which openings 202R have been formed in lowerlayer 202 is merely illustrative.

FIG. 27 is a cross-sectional side view of a layer of material 200 aboveair gap 64 that has been provided with recesses 200R and correspondingprotrusions 200P to form air flow promotion structures for display 14.Layer 200 may include one or more of display layers 52. Recesses 200Rand protrusions 200P may be formed by deforming display layers(structures 52) under heat and/or pressure in a press with patternedraised portions and depressions, using laser drilling, usingphotolithography, using machining equipment, by building layers ofmaterial such as protrusions onto the lower surface of structures 52using adhesive and additional layer(s) of material, or other suitabletechniques. FIG. 28 shows how surface deformation techniques (e.g.,compressing some or all of the layers of material in layer 202 with apress, etc.) can be used to create depressions such as recessed portions202R and protrusions 202P in layer 202. Arrangements of the type shownin FIG. 27 may be used alone, arrangements of the type shown in FIG. 28may be used alone, or arrangements of the type shown in FIGS. 27 and 28may be used together. The recesses in the opposing surfaces above and/orbelow air gap 62 may serve as air flow promotion channels or other airflow promotion structures and may, if desired, form anti-stick surfacesfor such structures, as described in connection with the structures ofFIGS. 7-25. Protrusions 200P and/or 202P may form spacer pads, may formanti-stick textures, and/or may form other air flow promotionstructures.

If desired, sensor structures such as electrodes 60 and 66, deformablelayer 62, etc. (see, e.g., some or all of layer 202 of FIG. 28) may beformed on the lower surface of display structures 52 and may be deformed(e.g., bent inwardly) under pressure from a finger or other externalobject. In this situation, layer 202 of FIG. 28 may be located above airgap 64 and other structures (e.g., a battery, internal housingstructures, and/or one or more other layers of material) may be locatedbelow air gap. When the outer sensor layers are bent inwardly bypressure from the user's finger, deformable layer 62 of the outer sensorlayers will contact the battery or other internal layer, therebydeforming a portion of layer 62 and decreasing the spacing betweenelectrodes 60 and 66 to produce a force signal. To promote airflow andto combat suction effects, air flow promotion structures (e.g., shims,deformations, etc.) may be formed on the lower surface of the structuresabove air gap 64 (e.g., the lower surface of the sensor layers) and/oron the opposing upper surface of the battery or other layer(s) under airgap 64.

As shown in FIG. 29, the recesses or other openings formed in the layersabove or below air gap 64 may pass through sensor electrodes. In theexample of FIG. 29, an array of capacitive force sensor electrodes 302has been formed on layer 300. Layer 300 may be formed above or below airgap 64 and may include structures such as some or all of the structuresof layers 200 and 202. In response to an applied external force, displaystructures or structures in device 10 may deform. This deformation maycause display structures or other structures to contact surface 308 oflayer 300. Air flow promotion structures may be formed from openingsthat pass through some or all of layer 300, as illustrated by holes 306and may include openings that pass through electrodes 302, asillustrated by holes 304. There may be any suitable number of holes suchas holes 304 and 306 (e.g., one or more holes may be formed perelectrode) and these holes may be circular, rectangular, or may haveother suitable shapes. The illustrative configuration of FIG. 29 isshown as an example.

The foregoing is merely illustrative and various modifications can bemade by those skilled in the art without departing from the scope andspirit of the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. An electronic device, comprising: first andsecond capacitive sensor electrodes separated by a deformable layer; alayer that is separated from the first capacitive sensor by an air gapand that deforms towards the first electrode when a force is applied byan external object; and air flow promotion structures interposed betweenthe layer and the first capacitive sensor electrode to enhance air flowin the air gap when the force has been removed from the layer and thelayer is moving away from the first electrode.
 2. The electronic devicedefined in claim 1 wherein the air flow promotion structures include atleast one spacer pad.
 3. The electronic device defined in claim 2wherein the spacer pad has a textured anti-stick surface.
 4. Theelectronic device defined in claim 2 wherein the spacer pad has ahydrophobic coating.
 5. The electronic device defined in claim 2 whereinthe spacer pad has an elastic modulus of at least 1 GPa and a height of10-100 microns.
 6. The electronic device defined in claim 2 wherein thespacer pad comprises a layer of polymer.
 7. The electronic devicedefined in claim 6 further comprising a layer of adhesive that attachesthe layer of polymer to the deformable layer.
 8. The electronic devicedefined in claim 2 wherein the air flow promotion structures include aplurality of spacer pads including the at least one spacer pad.
 9. Theelectronic device defined in claim 8 wherein the plurality of spacerpads include first spacer pads having a first height and second spacerpads having a second height that is different than the first height. 10.The electronic device defined in claim 1 wherein the deformable layercomprises an elastomeric polymer layer.
 11. The electronic devicedefined in claim 10 wherein the first electrode comprises one of aplurality of electrodes on the elastomeric polymer layer.
 12. Theelectronic device defined in claim 1 further comprising a display,wherein the layer that is separated from the first capacitive sensor bythe air gap comprises part of the display.
 13. The electronic devicedefined in claim 12 wherein the display includes a backlight unit andwherein the layer that is separated from the first capacitive sensor bythe air gap comprises part of the backlight unit.
 14. An electronicdevice operable by a user with an external object, comprising: ahousing; a display mounted in the housing, wherein the display hasdisplay layers that deform inwardly in response to pressure from theexternal object; a capacitive force sensor that measures force levelsapplied by the external object to the display cover layer by makingcapacitance measurements using electrodes separated by an elastomericlayer; and an array of spacer pads covering the elastomeric layer,wherein the display layers press against the array of spacer pads andcompress the elastomeric layer when the display layers are bentinwardly.
 15. The electronic device defined in claim 14 wherein thespacer pads include first spacer pads having a first height and secondspacer pads having a second height that is different than the firstheight.
 16. The electronic device defined in claim 15 wherein the firstand second spacer pads are arranged in a checkerboard pattern on theelastomeric layer.
 17. The electronic device defined in claim 14 furthercomprising touch sensor circuitry that makes position measurements onthe external object.
 18. An electronic device, comprising: a displaythat deforms inwardly when pressed with a force by an external object;an array of first capacitive electrodes on a first surface of anelastomeric layer; a second capacitive electrode on an opposing secondsurface of the elastomeric layer; force sensing circuitry that measuresthe force by measuring capacitances between the first capacitiveelectrodes and the second capacitive electrode; and an array of spacerpads on the first surface of the elastomeric layer that are contacted byan inner surface of the display when the display deforms inwardly andthereby deforms the elastomeric layer and increases the measuredcapacitances.
 19. The electronic device defined in claim 18 wherein thespacer pads include polymer layers.
 20. The electronic device defined inclaim 19 wherein the spacer pads have anti-stick surfaces.
 21. Anelectronic device having an outer surface, comprising: first and secondcapacitive sensor electrodes separated by a deformable layer that isoverlapped by the outer surface; a layer that is separated from thedeformable layer by an air gap, wherein the deformable layer and thelayer that is separated from the deformable layer contact each otheracross the air gap when a force is applied to the outer surface by anexternal object; and air flow promotion structures that enhance air flowin the air gap when the force has been removed from the layer and thelayer is moving away from the first electrode.
 22. The electronic devicedefined in claim 21 wherein the air flow promotion structures compriseopenings in the deformable layer.
 23. The electronic device defined inclaim 21 wherein the air flow promotion structures comprise recesses inthe deformable layer.
 24. The electronic device defined in claim 21wherein the recesses comprise deformations in the deformable layer. 25.The electronic device defined in claim 21 wherein the air flow promotionstructures comprise deformations in the layer that is separated from thedeformable layer by the air gap.
 26. The electronic device defined inclaim 21 further comprising a display, wherein the deformable layer isattached to the display.
 27. The electronic device defined in claim 26wherein the air flow promotion structures comprise an array of spacerpads on the deformable layer.
 28. The electronic device defined in claim21 further comprising a display, wherein the layer that is separatedfrom the deformable layer is attached to the display.
 29. The electronicdevice defined in claim 21 wherein the air flow promotion structuresinclude at least one hole that passes through the first capacitor sensorelectrode.